This invention relates to an endoscope apparatus, and more specifically to an endoscope apparatus capable of measuring the size of an affected part of a subject.
Conventionally, in observing the interior of a body cavity by means of an endoscope, the size of an affected part of a subject image observed within the field of view of an optical system for observation varies with the change of the distance between the objective lens of the endoscope and the subject. Namely, the affected part looks greater as the objective lens approaches closer to the affected part, whereas it looks smaller when the objective lens is far from the affected part. Thus, the actual size of the affected part cannot be measured from the image in the field of view. Accordingly, there have been proposed various expedients for measuring the actual dimensions of the affected part. Some of these expedients are as follows:
(1`) A spot light is diagonally applied at a given angle to the optical axis of the objective lens, the distance between the position of the spot light in the field of view and the subject is measured, and the measured size of the affected part is calculated using the measured distance as a conversion factor for actual size.
(2) A flexible scale with graduations is inserted through a forceps channel to be held against the affected part, and is observed through the endoscope for reading.
(3) The moved distance of e.g. the objective lens moved for the focusing of the optical system for observation is measured, and the size of the affected part is calculated on the basis of the moved distance.
In conjunction with (1), however, the objective lens is wide-angled for ease of orientation in the body cavity, so that the aberration of the objective lens is too great for accurate measurement of the distance between the objective lens and the subject. In some cases, therefore, the measurement error may amount to 30% to 40%. The expedient (2) is not a perfect measure because the operation of holding the scale against the affected part is too hard a task to ensure quick measurement. In connection with (3), moreover, the depth of field of the optical system for observation is substantial because it cannot practically be reduced so much. Accordingly, even though the moved distance of the objective lens is detected, the measured value obtained will be subject to an error corresponding to such depth of field, and the size of the affected part will not be able to be measured with accuracy.